1: In reality, it's bringing a male close to climax (close enough where his testicles get filled with seminal fluid and semen), but not letting him get rid of the built-up sex juices.
The resulting inundation causes extreme discomfort and pain, lasting for hours.
See also blue ball2: In slang terms, it's the expectation and tremendous build-up of getting something you want, only to find that you're not going to get it in the end.

2: I'm sorry to blueball you, but remember how I said you're getting a Corvette, yeah, you're actually getting a Yugo...

Blue balls happens when your with someone, kissing or something, and you are aroused for a long period of time, but you never ejaculate. Your balls may get bigger, or even shrink a little, and there is a slight bluish greyish color sometimes.
The pain is pretty bad. If you walk around, your balls and stomach hurts, but for a long time. It feels like you were kicked in the nuts, like when you get that stomach hurting feeling after being kicked there.
To cure: Have your partner finish you, or (God forbid), you gotta jack off. Without cumming, your balls can hurt for awhile. You gotta be careful not to go to fast because it hurts. IMPORTANT: This is kinda funny, but when you jack off after having blue balls, you will cum SO MUCH!! When I dont got blue balls, I cum like one solid piece, but with bllue balls I shot out like (No kidding), 5 good, solid shots. Be ready. Kinda like a cheap porno.

YOU: After Jenna came over, we kissed for awhile, but she left before we could do it.